UNS S66286 Forgings

UNS S66286, usually called A-286, is an age-hardenable iron-nickel-chromium superalloy. It holds high strength and creep resistance up to about 700 °C (1,300 °F), and it is non-magnetic and oxidation resistant. Ageing precipitates a γ′ Ni₃(Al,Ti) phase. Because the strengthening does not depend on cold work, heavy sections reach the same properties as thin ones. Thermal expansion is close to that of austenitic stainless steel, which is why the alloy is used for hot bolting and for fasteners that have to stay tight through thermal cycling.

Jiangyin Jiangnan Metal Co., Ltd. forges UNS S66286 into seamless rolled rings, round bars, discs, shafts, flanges, sleeves and extrusion tooling at its open-die forging plant in Jiangyin, Jiangsu, China. Forgings are supplied solution annealed and aged, ultrasonically tested to ASTM A388 or EN 10228-3, and certified to EN 10204 3.1 or 3.2. Send a drawing to sales@steelforgepieces.com for a written quotation within 24 hours.

UNS S66286 is the reference chemistry. The designations below all describe the same alloy, and each standard adds its own heat treatment, testing and dimensional requirements. Order against the end specification, for example AMS 5737 or ASTM A453 Grade 660 Class D. A trade name on its own does not fix the heat treatment.

Melting is by electric arc furnace with AOD or VOD refining, followed by electroslag remelting (ESR). Vacuum induction melting with vacuum arc remelting (VIM + VAR) is available where the specification calls for it, which is normally the case for aerospace rotating parts.

The values below are acceptance minima at room temperature in the solution annealed and aged condition. Production forgings normally test above these figures.

The bolting specifications add a stress-rupture test at 650 °C (1,200 °F) alongside the room-temperature tensile test. This is the test that picks up incomplete or incorrect ageing.

UNS S66286 is hot worked between about 1,150 °C and 900 °C. Below 900 °C it work-hardens sharply and will crack, so heavy sections are reheated between passes. Finishing temperature controls grain size, which in turn affects notch toughness and creep life.

Two solution annealing temperatures are in common use, and they do not produce the same part:

• Solution annealing at 980 °C (1,800 °F), oil quenched. Coarser grain, better creep and stress-rupture life. Specified for ASTM A453 Classes B, C and D.
• Solution annealing at 900 °C (1,650 °F), oil quenched. Finer grain, better room-temperature ductility and notch toughness. Specified for ASTM A453 Class A, ASTM A638 Type 1 and AMS 5737.
• Ageing at 720 °C (1,325 °F) for 16 hours, air cooled. This precipitates the γ′ Ni₃(Al,Ti) phase that carries the strength.

State the class or the end specification on the enquiry. The same chemistry gives measurably different properties depending on which route is used.

All items are forged to customer drawing, open-die or ring-rolled, in single pieces or production batches. Machining allowance is added to finished dimensions unless the drawing already gives forging sizes.

Each forging is supplied with a mill test certificate traceable to the heat number, which is hard-stamped on the part.

• Ultrasonic testing to ASTM A388, EN 10228-3 or SEP 1921, to the acceptance class stated on the order.
• Chemical analysis by spectrometer on the heat, with product analysis on request.
• Mechanical testing: tensile, yield, elongation, reduction of area, hardness and Charpy impact, at room or elevated temperature.
• Stress-rupture testing at 650 °C where ASTM A453, ASTM A638 or the AMS specification calls for it.
• Metallography: grain size to ASTM E112, micro and macro examination.
• Dimensional report against the drawing, with a marked-up copy returned.
• Certification to EN 10204 3.1, or EN 10204 3.2 witnessed by TUV, SGS, BV, Lloyd's Register or your own inspector.

Turbine discs, casings, shafts, fasteners and afterburner hardware carrying load at 600–700 °C. A-286 has been used for aero-engine fasteners since the 1950s and is still standard for the cooler stages.

Wellhead and Christmas tree components, valve stems, seat rings and bodies, subsea and deepwater production hardware, and non-magnetic drill collar parts. Low magnetic permeability also makes the alloy suitable for downhole instrumentation housings.

Steam and gas turbine bolting, generator retaining-ring components, industrial air compressor parts, nitrogen generator internals, and nuclear engineering hardware where non-magnetic behaviour is required.

Forged flanges, tube sheets, forged pipe and tube, shell-and-tube heat exchanger parts, air receivers, industrial furnace and heat-treatment fixtures, retorts and crystalliser equipment.

Exhaust manifold and turbocharger fasteners, valve train parts, and engine components exposed to sustained heat and vibration.

A-286 keeps its toughness and remains non-magnetic down to liquid helium temperature. Applications include superconducting magnet structures, LNG hardware and cryogenic test rigs.

Below about 550 °C a precipitation-hardening stainless such as 17-4PH is cheaper and adequate. Above about 700 °C the γ′ coarsens and strength falls away, and a nickel-base alloy is required. Between those temperatures A-286 is usually the most economical choice, since it is roughly 53% iron rather than 50 to 70% nickel.

Other age-hardenable and heat-resistant grades we forge to the same standards: